Dang Nature You're Neat (2000 P Quarter).

So the two black images are both sides of the same coin?

Your coin looks to match number 1 in the list of Dirty Dozen Damages. Even though there is no premium value to these, you might try to find a nice example of each.

1) discoloration - stains from a beverage, or environmental damage from being buried, heated, etc.
2) scrapes over much of the coin - damage from sliding on pavement, a parking lot coin
3) coin bent or edges not round - it has been smashed with a hammer
4) coin blank on all or most of one side - someone machined the surface away or sanded it down
5) mirrored lettering - a vise job, a coin squeezed against another in a vise
6) rough, pebbly surfaces - a coin eroded by acid, it might now be underweight
7) smooth rims, smaller diameter - was trapped rolling inside a dryer, a " Dryer Coin", or tapped with a spoon
8) clear mounds on coin - glue that has dried transparently
9) small indentations in the shape of the letter D - marks left by the impact of the reeded edge of another coin
10) large blisters - coin exposed to high heat, such as in a campfire
11) shapes, often letters or numbers, not indented or raised - Pareidolia (like animal shapes in a cloud)
12) a circular scrape just inside the rim - " Ring of Death" caused by a coin rolling or vending machine

Don't despair! Error coins remain ready to find from circulation, but they are outnumbered by unusual looking coins that merely have been damaged. If you can imagine a way to change an undamaged coin into one like you see, that's probably exactly what happened to it. Changes to a coin after it leaves the mint's striking chamber are considered post mint damage, or PMD, and have no premium value.

The alloy used for nickels and the outer clad layers on dimes, quarters, and halves are susceptible to environmental damage also resulting in a darker appearance. Unless you are getting them from mint bags or rolls it would be hard to know exactly what its been exposed to during its circulation. They can also develop toning.

Here are some of the things I've read that can cause a coin to tone dark or can cause a coin to turn a variety of colors, from deep grey or black to mottled or speckled.

Experimentation with acid, or just normal corrosion
Burial in the ground
Being tossed in a water fountain
Exposure to intense heat, or very cold temperatures
Storage in a paper envelope, PVC plastic, or open-air case
Contact with caustic chemicals or fumes, such as sulfur or gas
Sitting in a warm and humid environment for long periods of time
Placed in old fashioned coin folders or albums can also cause toning, potentially attractive, with colors ranging from light blues and pinks even to rainbow colors.

Yes there are also dark colored coins that may have come that way from the mint, Black beauty nickels as one example seem to be the result of improper annealment, the process by which planchets are heated to prepare them for striking. It seems these nickels were left in the furnace a bit too long, producing a darker color that can range from gunmetal gray to jet black. Some also think they may have an improper alloy mix. Improper annealment can be found in all denominations actually, but 1959 nickels are particularly known for this error.